Standards for WLAN (Wireless Local Area Network) technologies include IEEE 802.11 standards. Among amendments of the IEEE 802.11 standards, IEEE 802.11a/b provide transmission rates of 11 Mbps (IEEE 802.11b) and 54 Mbps (IEEE 802.11a) using an unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11g provides a transmission rate of 54 Mbps using OFDM at 2.4 GHz. IEEE 802.11n provides a transmission rate of 300 Mbps for 4 spatial streams using MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing). IEEE 802.11n supports channel bandwidths of up to 40 MHz and, in this case, provides a transmission rate of 600 Mbps.
On the other hand, IEEE 802.11ad provides a standard for supporting a very high throughput at a band of 60GHz, and provides a Fast Session Transfer (FST) function as one exemplary method for providing the above standard.
Provided that one STA can be operated in a plurality of bands, respective STAs are shifted to other bands as necessary and can be operated in the shifted bands. In this case, the term “band” may be, for example, a band of 2.4 GHz, 5 GHz, 60 GHz or 900 MHz and a TV white space (TVWS) band of 400˜700 MHz. However, if there is an additional frequency band in which the IEEE 802.11 system can be used, the corresponding band may also be contained in the scope of the term “band”.
For example, if there are STAs capable of supporting the 2.4 GHz and 60 GHz bands, one of STAs being operated in the 2.4 GHz band may be shifted to another band (i.e., the 60 GHz band) so as to provide a higher data transmission/reception rate to other STAs. Specifically, provided that an access point (AP) generates such request and supports two bands, when an STA that has already been associated at 2.4 GHz switches to 60 GHz, the STA need not perform additional association at the corresponding band. Such band switching is referred to as a fast session transfer (FST).
In brief, the term “FST” means, assuming that STAs can be operated in desired frequency band(s), that sessions of STAs are shifted from one channel to another channel within the same or different frequency bands.
However, if an STA capable of supporting multiple bands including a white space (for example, TVWS) requests to switch to a TVWS, the above-mentioned FST must additionally consider some factors. In more detail, the white space band can enable unlicensed devices to perform communication so long as communication of licensed devices is not interrupted in the corresponding band, so that the above-mentioned FST must consider some factors.